1. Field of the Invention
The present invention relates to a process for producing a halogenated benzene compound, the process comprising the step of reacting in a solvent an organometallic compound with a halide ion (X.sup.-), under light irradiation conditions in the presence of a semiconductor catalyst with a photocatalytic activity, particularly to a process useful for producing a halogenated benzene compound labeled with a radioactive halogen.
2. Description of the Related Art
Halogenated benzene compounds have an important role as various biologically active substances typified by drugs and agrochemicals and as intermediates for their synthesis. Further, compounds including a radioactive halogen in their molecules have extremely valuable as a radioactive tracer which is used for elucidating in-vivo behavior of drugs and the like in the course of their development, or as in-vivo or in-vitro diagnostic or therapeutic drugs for clinical diagnosis or therapy. Among the compounds including a radioactive halogen in their molecules to be used for these purposes, N-isopropylamphetamine hydrochloride labeled with iodine-123 is used as an in-vivo diagnostic drug for brain functions, 15-(p-iodophenyl)-3-(R,S)-methylpentadecanoic acid is used as that for heart diseases, and an iodohippuric acid sodium salt is used as that for kidney and urinary tract diseases, for example.
In recent years, a labeling method utilizing the exchange of a metal such as tin, silicon and germanium with a halogen has been widely used as a technique for producing such compounds including a radioactive halogen in their molecules because products with high specific radioactivities can be obtained in high position selectivities. However, since raw materials to be used for labeling are generally available with stability in the form of halide ions, the above method requires complicated operations, for example, of conducting the reaction in the presence of an oxidizing agent (sometimes, in large excess) such as hypochlorite, chloramine T (N-chloro-4-methylbenzenesulfonamide sodium salt), Iodo-Gen.TM. (1,3,4,6-tetrachloro-3.alpha.,6.alpha.-diphenylglycoluril), Iodo-beads.TM. (N-chloro-benzenesulfonamide (sodium salt) derivatized, uniform, nonporous, polystyrene beads), hydrogen peroxide and NBS (1-Bromosuccinimide), and of removing the remaining oxidizing agent by, for example, adding a reducing agent at the completion of the reaction.
Further, in the above method, the compound to be labeled is exposed to oxidizing conditions. Therefore, it is difficult to apply the method when the compound to be labeled is unstable in such conditions.